Engine sound management

ABSTRACT

In a vehicle equipped with a vehicle sound system, determining a virtual fixed gear ratio; determining a virtual RPM based on the virtual fixed gear ratio; generating a set of harmonic signals based on the virtual RPM, the harmonic signals being sine-wave signals proportional to harmonics of the virtual RPM; processing the harmonic signals to produce a set of processed harmonic signals; and in the vehicle sound system, transducing the processed harmonic signals to acoustic energy thereby to produce an engine sound within a passenger cabin of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/092,202, filed Apr. 6, 2016 which is a continuation of U.S.application Ser. No. 14/152,538, filed Jan. 10, 2014, now U.S. Pat. No.9,333,911, each of which is incorporated herein by reference in itsentirety.

BACKGROUND

This disclosure relates to sound management.

A considerable sound problem exists in vehicles equipped withContinuously Variable Transmission (CVT), i.e., when the vehicleaccelerates a constant pitch is emitted for the engine. This soundproblem is more pronounced for small displacement engines, which have alower torque, and therefore, are more likely to operate under constantRPM conditions while accelerating.

In CVT equipped vehicles, an operator may notice that at some pointduring an acceleration cycle, an engine RPM reaches a value that staysrelatively constant. At the same time, a speed of the vehicle continuesto rise. When the operator requests the vehicle to accelerate and feelsthe acceleration, the sound of the CVT power train provides an incorrectsound feedback, suggesting that the vehicle is not accelerating. This isnot just a power train (PT) sound quality problem, but can also be asafety issue, since the operator may be tempted to further accelerate.

A similar sound problem exists in electric vehicles and hybrid vehiclesrunning in an electric mode.

SUMMARY

In one aspect, a method includes, in a vehicle equipped with a vehiclesound system, determining a virtual fixed gear ratio; determining avirtual RPM based on the virtual fixed gear ratio; generating a set ofharmonic signals based on the virtual RPM, the harmonic signals beingsine-wave signals proportional to harmonics of the virtual RPM;processing the harmonic signals to produce a set of processed harmonicsignals; and in the vehicle sound system, transducing the processedharmonic signals to acoustic energy thereby to produce an engine soundwithin a passenger cabin of the vehicle.

Implementations may include one of the following features, or anycombination thereof.

In some examples, the vehicle is equipped with a continuously variabletransmission, and the virtual fixed gear ratio is determined based on acurrent gear ratio of the continuously variable transmission whichvaries continuously in time as a function of an actual, measured RPM andvehicle speed. The virtual RPM changes with the vehicle speed when theactual RPM remains constant.

In some implementations, the virtual fixed gear ratio is determinedaccording to: GR_(virtual)(t)=c·ƒ(GR_(CVT)(t)), where GR_(virtual)(t) isthe virtual fixed gear ratio; c is a constant; GR_(CVT)(t) is thecurrent gear ratio of the CVT; and ƒ(GR_(CVT)(t)) is a mapping functionfor mapping the current gear ratio to a set of predefined virtual fixedgear ratios.

In certain implementations, the virtual fixed gear ratio is determinedaccording to: GR_(virtual)(t)=c(t)·ƒ(GR_(CVT) (t)), whereGR_(virtual)(t) is the virtual fixed gear ratio; c(t) is a variable thatvaries as a function of a measured engine load; GR_(CVT)(t) is thecurrent gear ratio of the CVT; and ƒ(GR_(CVT)(t)) is a mapping functionfor mapping the current gear ratio to a set of predefined virtual fixedgear ratios.

In some examples, virtual fixed gear ratio is determined according to:GR_(virtual) (t)=c(t)·ƒ(GR_(CVT)(t)), where GR_(virtual)(t) is thevirtual fixed gear ratio; c(t) is a variable that varies as a functionof a measured accelerator pedal position; GR_(CVT)(t) is the currentgear ratio of the CVT; and ƒ(GR_(CVT)(t)) is a mapping function formapping the current gear ratio to a set of predefined virtual fixed gearratios.

In certain examples, the virtual fixed gear ratio is determinedaccording to: GR_(virtual)(t)=c(t)·ƒ(GR_(CVT)(t)), where c(t) is avariable that varies as a function of a measured engine load and ameasured accelerator pedal position, and ƒ(GR_(CVT)(t)) is a mappingfunction for mapping the current gear ratio (GR_(CVT)(t)) to a set ofpredefined virtual fixed gear ratios.

In some cases, determining the virtual fixed gear ratio includes mappingthe current gear ratio to one of a set of predefined fixed gear ratiosaccording to a mapping function. The mapping function ƒ(GR_(CVT)(t)) isexpressed as:

${f\left( {{GR}_{CVT}(t)} \right)} = \left\{ {\begin{matrix}{{\mathcal{g}}\; r_{1}} & {,{if}} & {{th}_{1} \leq {{GRcvt}(t)}} \\{{\mathcal{g}}\; r_{2}} & {,{if}} & {{th}_{2} \leq {{GRcvt}(t)} \leq {th}_{1}} \\\; & \vdots & \; \\{{\mathcal{g}}\; r_{N}} & {,{if}} & {{{GRcvt}(t)} \leq {th}_{N}}\end{matrix},} \right.$

where GR_(CVT)(t) is the current gear ratio of the CVT; {gr_(n)} is theset of predefined fixed gear ratios; and {th_(n)} is a set of predefinedgear ratio thresholds.

In some cases, the method includes determining the current gear ratioaccording to:

${{{GR}_{CVT}(t)} = {\frac{{RPMactual}(t)}{{VSP}(t)} \cdot {CR}}},$where GR_(CVT)(t) is the current gear ratio of the CVT; and CR is aconstant that captures fixed transmission ratios external to the CVT.

In some implementations, the method includes determining if soundcorrection is necessary. If sound correction is necessary, then themethod also includes calculating an instantaneous value of the currentgear ratio of the CVT, setting the virtual fixed gear ratio to theinstantaneous value of the current gear ratio of the CVT and maintainingthe virtual gear ratio constant at the calculated instantaneous value ofthe current gear ratio until a gear ratio deviation of the virtual fixedgear ratio relative to the current gear ratio exceeds a gear ratiodeviation value.

In certain implementations, the method includes determining the gearratio deviation according to:

${{\Delta\;{{GR}(t)}} = {c \cdot \frac{{{GR}_{virtual}(t)} - {{GR}_{CVT}(t)}}{{GR}_{virtual}(t)}}},$where ΔGR(t) is the gear ratio deviation; GR_(virtual)(t) is the virtualfixed gear ratio; GR_(CVT)(t) is the current gear ratio of the CVT; andc is a constant.

In some examples, the method includes determining the gear ratiodeviation according to:

${{\Delta\;{{GR}(t)}} = {{c(t)} \cdot \frac{{{GR}_{virtual}(t)} - {{GR}_{CVT}(t)}}{{GR}_{virtual}(t)}}},$where ΔGR(t) is the gear ratio deviation; GR_(virtual)(t) is the virtualfixed gear ratio; GR_(CVT)(t) is the current gear ratio of the CVT; andc(t) is a variable that varies as a function of a measured engine load.

In certain examples, the method includes determining the gear ratiodeviation according to:

${{\Delta\;{{GR}(t)}} = {{c(t)} \cdot \frac{{{GR}_{virtual}(t)} - {{GR}_{CVT}(t)}}{{GR}_{virtual}(t)}}},$where ΔGR(t) is the gear ratio deviation; GR_(virtual)(t) is the virtualfixed gear ratio; GR_(CVT)(t) is the current gear ratio of the CVT; andc(t) is a variable that varies as a function of accelerator pedalposition.

In some cases, the method includes determining the gear ratio deviationaccording to: ΔGR(t)=c·(GR_(virtual)(t)−GR_(CVT)(t)), where ΔGR(t) isthe gear ratio deviation; GR_(virtual)(t) is the virtual fixed gearratio; GR_(CVT)(t) is the current gear ratio of the CVT; and c is aconstant.

In certain cases, the method includes determining the gear ratiodeviation according to: ΔGR(t)=c(t)·(GR_(virtual)(t)−GR_(CVT)(t)), whereΔGR(t) is the gear ratio deviation; GR_(virtual)(t) is the virtual fixedgear ratio; GR_(CVT)(t) is the current gear ratio of the CVT; and c(t)is a variable that varies as a function of a measured engine load.

In some implementations, the method includes determining the gear ratiodeviation according to: ΔGR(t)=c(t)·(GR_(virtual)(t)−GR_(CVT)(t)), whereΔGR(t) is the gear ratio deviation; GR_(virtual)(t) is the virtual fixedgear ratio; GR_(CVT)(t) is the current gear ratio of the CVT; and c(t)is a variable that varies as a function of a measured accelerator pedalposition.

In certain implementations, determining if sound correction is necessaryincludes determining that ΔRPM does not exceed a maximum value Rmax, anddetermining that ΔVSP exceeds a minimum value, Vmax.

In some examples, determining if sound correction is needed includesdetermining that ΔRPM exceeds a minimum value Rmin.

In certain examples, the virtual fixed gear ratio is determinedaccording to:

${{GR}_{virtual}(t)} = \left\{ {\begin{matrix}{{{GR}_{virtual}\left( {t - 1} \right)},{{if}\mspace{14mu}{correction}\mspace{14mu}{needed}},{{{and}\mspace{14mu}\Delta\;{{GR}\left( {t - 1} \right)}} < A}} \\{{{GR}_{CVT}(t)},{otherwise}}\end{matrix},} \right.$where GR_(virtual)(t) is the virtual fixed gear ratio; GR_(virtual)(t−1)is a previously determined virtual fixed gear ratio determined at timet−1; GR_(CVT)(t) is the current gear ratio of the CVT; and the parameterA is tunable and represents the desired vs. actual gear ratio deviationthat will trigger a gear shift.

In some cases, the virtual RPM is determined according to:RPM_(virtual)(t)=GR_(virtual)(t)·VSP(t)·CR⁻¹, where RPM_(virtual)(t) isthe virtual RPM; GR_(virtual)(t) is the virtual fixed gear ratio; VSP(t)is the vehicle speed; and CR is a constant that captures fixedtransmission ratios external to the CVT.

In certain cases, the method includes generating a set of harmoniccancellation signals based on the actual RPM, the harmonic signals beingsine-wave signals proportional to harmonics of the actual RPM;processing the harmonic cancellation signals to produce a set ofprocessed harmonic cancellation signals; and, in the vehicle soundsystem, transducing the processed harmonic cancellation signals toacoustic energy thereby to produce an engine sound within a passengercabin of the vehicle,

In some implementations, processing the harmonic cancellation signalsincludes, for each of the harmonic cancellation signals of the set ofharmonic cancellation signals, modifying the amplitude and/or phase ofthe harmonic cancellation signal with an adaptive filter.

In certain implementations, processing the harmonic cancellation signalsincludes, for each of the harmonic cancellation signals of the set ofharmonic cancellation signals, adjusting an amplitude of the harmoniccancellation signal as a function of a measured engine load oraccelerator pedal position.

In certain examples, processing the harmonic signals includes for eachof the harmonic signals of the set of the harmonic signals, applying acorresponding gain as a function of the virtual RPM.

In some cases, processing the harmonic signals includes for each of theharmonic signals of the set of the harmonic signals, applying a gain asa function of a measured engine load or accelerator pedal position.

In certain cases, the vehicle is equipped with an electric motor, andthe virtual RPM can then be determined based on vehicle speed andpredefined virtual gear ratios.

In some implementations, the vehicle is a hybrid vehicle capable ofoperating in an internal combustion (IC) mode and an electric vehicle(EV) mode. When operating in the EV mode the virtual RPM is determinedbased on vehicle speed and a first set of predefined virtual gearratios, and, when operating in IC mode the virtual RPM is determinedbased on an actual RPM measured from an internal combustion engine ofthe hybrid vehicle, vehicle speed, and a second set of predefinedvirtual gear ratios.

In another aspect, a method includes: in a vehicle equipped with acontinuously variable transmission (CVT) and a vehicle sound system,determining if sound correction is necessary. If sound correction is notnecessary, then the method also includes generating a set of harmonicsignals based on an actual, measured RPM, the harmonic signals beingsine-wave signals proportional to harmonics of the actual RPM. If soundcorrection is necessary, then the method also includes determining avirtual fixed gear ratio based on a current gear ratio of thecontinuously variable transmission which varies continuously in time asa function of an actual, measured RPM and vehicle speed; determining avirtual RPM based on the virtual fixed gear ratio generating a set ofharmonic signals based on the virtual RPM, the harmonic signals beingsine-wave signals proportional to harmonics of the virtual RPM;processing the harmonic signals to produce a set of processed harmonicsignals; and in the vehicle sound system, transducing the processedharmonic signals to acoustic energy thereby to produce an engine soundwithin a passenger cabin of the vehicle. The virtual RPM changes withthe vehicle speed even when the actual RPM remains constant.

Implementations may include one of the above and/or below features, orany combination thereof.

In some implementations, determining if sound correction is necessaryincludes determining that ΔRPM does not exceed a maximum value Rmax, anddetermining that ΔVSP exceeds a minimum value Vmax.

In certain implementations, determining if sound correction is neededfurther includes determining that ΔRPM exceeds a minimum value Rmin.

Another aspect features a method that includes, in a vehicle equippedwith a vehicle sound system, providing harmonics of a fundamentalfrequency which increases with time; and generating an increasing pitchvia the vehicle sound system by transducing the harmonics in a limitedfrequency range. Generating the increasing pitch includes separatelydecreasing amplitudes of the harmonics as each of the harmonics approachan upper limit of the frequency range such that the harmonics becomeinaudible as they individually reach the upper limit of the frequencyrange. As one of the harmonics becomes inaudible, another one of theharmonics becomes audible.

Implementations may include one of the above and/or below features, orany combination thereof.

In some implementations, the fundamental frequency is representative ofan actual, measured vehicle RPM that increases with time.

In certain implementations, the vehicle is equipped with an electricmotor, and the fundamental frequency is representative of an actual RPMof the electric motor.

In some examples, the fundamental frequency is representative of avirtual RPM which is determined based on a set of predefined virtualfixed gear ratios.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an exemplary engine sound managementsystem;

FIG. 1B is a block diagram of an engine harmonic management (EHX)sub-system from the engine sound management system of FIG. 1A.

FIG. 2 is an exemplary graph illustrating a sample gear ratio mappingused in the engine sound management system;

FIG. 3 is table illustrating one exemplary set of criteria; and

FIG. 4 is a flow diagram of an exemplary control RPM (RPM_(control))selection process used in the engine sound management system.

FIGS. 5A, 5B, and 6 are spectrograms illustrating psychoacousticapproaches to pitch shifting.

DETAILED DESCRIPTION

This disclosure is based, at least in part, on the realization that, ina vehicle which includes a continuously variable transmission, aperceived engine sound can be correlated with a vehicle's accelerationsuch that the engine sound pitch increases as long as the vehicleaccelerates. This can be achieved by introducing a disruption in thesignal that controls pitch, i.e., the engine speed (RPM). The disruptioncan be introduced at least during acceleration cycles when the RPMremains constant.

The disruption can be thought of as being introduced by a virtual,desired RPM, corresponding to a virtual, desired powertrain (virtualgearbox). The virtual gearbox is used, and tuned, for achieving thedesired variation in the sound of the vehicle.

Though the elements of several views of the drawing may be shown anddescribed as discrete elements in a block diagram and may be referred toas “circuitry,” unless otherwise indicated, the elements may beimplemented as one of, or a combination of, analog circuitry, digitalcircuitry, or one or more microprocessors executing softwareinstructions. The software instructions may include digital signalprocessing (DSP) instructions. Operations may be performed by analogcircuitry or by a microprocessor executing software that performs themathematical or logical equivalent to the analog operation. Unlessotherwise indicated, signal lines may be implemented as discrete analogor digital signal lines, as a single discrete digital signal line withappropriate signal processing to process separate streams of signals, oras elements of a wireless communication system. Some of the processesmay be described in block diagrams. The activities that are performed ineach block may be performed by one element or by multiple elements, andmay be separated in time. The elements that perform the activities of ablock may be physically separated. Unless otherwise indicated, signalsmay be encoded and transmitted in either digital or analog form;conventional digital-to-analog or analog-to-digital converters may notbe shown in the figures.

As shown in FIG. 1A, an exemplary engine sound management system 100includes an engine control unit (ECU) 102 operationally linked to avehicle controller area network (CAN) bus 104. The CAN bus 104 isoperationally linked to an engine sound control module 106. The enginesound control module 106 is operationally linked to a vehicle soundsystem 108.

The ECU 102 monitors various vehicle engine load parameters, such asactual vehicle speed (VSP), actual engine revolutions per minute (RPM),and so forth. Some of these monitored parameters, such as vehicle speed,engine RPM and engine state parameters, for example, may be used asinput by the engine sound control module 106.

The engine sound control module 106 enables a change of an engine soundby canceling some harmonics, enhancing other harmonics, and generatingnew harmonics, in such a way that a perceived pitch of the engine soundis changing. This disclosure describes the control algorithm that can beused to drive the sound changes.

The engine sound control module 106 includes input control logic 110 andan engine harmonic management (EHX) sub-system 112. The input controllogic 110 provides a signal representative of a control RPM M(RPM_(control)) 114, a signal representative of control parameters 116,and a signal representative of the actual, measured engine RPM(RPM_(actual)) 118 as input to the EHX sub-system 112. Signals producedby the EHX sub-system 112, based on the input received from the inputcontrol logic 110, are transduced to acoustic energy by one or morespeakers within the vehicle sound system 108 positioned within aninterior of a vehicle and provide a desired sonic experience.

The input control logic 110 includes a virtual gearbox and RPMcomputation module 120 which provides the control RPM (RPM_(control))114, as will be discussed below, and a load processing module 122 whichprovides the control parameters 116.

All or some of the engine sound control module 106, input control logic110, the virtual gearbox and RPM computation module 120, the loadprocessing module 122, and the EHX sub-system 112 may be implemented assoftware instructions executed by one or more microprocessors or DSPchips, which may be components of an amplifier.

The EHX sub-system 112 includes an engine harmonics generation (EHG)module 124, a level control module 126 and an engine harmonicscancellation (EHC) module 128. The EHG module 124 receives the controlRPM 70 from the virtual gearbox and RPM computation module 120. All orsome of the EHG module 124, the level control module 126, and the EHCmodule 128, may be implemented as software instructions executed by oneor more microprocessors or DSP chips, which may be components of anamplifier.

Referring to FIG. 1B, the EHG module 124 includes a harmonics generator130 for generating sine-wave signals proportional to certain harmonics(i.e., harmonics, which could include non-integer harmonics, of afundamental frequency) of the control RPM. The harmonics generator 130determines and outputs two parameters for each harmonic. To determinethe first parameter, the harmonics generator 130 computes the frequencyfor each harmonic of the control RPM by multiplying the fundamentalfrequency by the order of each harmonic and outputs a sinusoid signal atthe frequency. To determine a second parameter, the harmonics generator130 converts the fundamental frequency into an index to a harmonicshape, that is, it determines a sound pressure level (SPL) for eachharmonic as the SPL varies with RPM. Typically, the harmonic shape isexpressed as a Look-Up Table (LUT). Alternately, the harmonic shape maybe calculated or approximated according to a formula.

The EHG module 124 also includes harmonic shape determiners 132 (oneshown for simplicity) and harmonic gains 134 (one shown for simplicity)for each harmonic generated. The harmonic shape determiners 132 aretypically implemented as frequency-to-gain look-up tables (LUTs), whichenables the sound level of each harmonic to be frequency dependent.Alternatively, the harmonic shape may be calculated or approximatedaccording to a formula. This shape control outputs a gain which adjuststhe level of the corresponding harmonic. The resulting harmonic signalproduces a sound level that matches a desired target. To achieve thisgoal the look-up table must account for the inherent harmonic level, thetarget harmonic level, and the transfer function of the vehicle soundsystem.

The harmonic gains 134 (one shown for simplicity) apply individualharmonic specific gains to each of the harmonic signals, based on inputfrom the harmonic shape LUTs 132 and the instantaneous values of thesinusoids for each of the harmonic frequencies determined by theharmonics generator 130. The EHG module 124 can also include otherharmonic gains 136 which can be utilized for adjusting the respectivelevels of the individual harmonic signals based on load.

The gain adjusted harmonic signals are then provided to the vehiclesound system 108 and transduced to acoustic energy by the speakers. Insome cases, the gain adjusted harmonic signals may be combined into aharmonic control signal and the harmonic control signal is provided tothe vehicle sound system 108. When the control RPM corresponds to theactual engine RPM, the EHG module 50 will provide engine harmonicenhancement of certain harmonics of the actual engine RPM. When thecontrol RPM is a virtual RPM, as will be discussed below, the EHG module50 will generate sine-wave signals proportional to certain harmonics ofthe virtual RPM.

All or some of the harmonics generator 130, the harmonic shapedeterminers 132, the harmonic gains 132, and the other harmonic gains134, may be implemented as software instructions executed by one or moremicroprocessors or DSP chips, which may be components of an amplifier.

The EHC module 128 receives an actual, measured engine RPM 118 (i.e., asignal representative of the actual, measured engine RPM) from the inputcontrol logic 110. The EHC module 128 includes a harmonic cancellationreference signal generator 138 for generating harmonic cancellationsignals, which are sine-wave reference signals proportional to certainharmonics of the actual measured engine RPM (RPM_(actual)).

The EHC module 128 also includes adaptive filters 140 for modifying therespective phases and/or amplitudes of the individual harmoniccancellation signals, based on input from one or more microphones 142(one shown) mounted in the passenger cabin of the vehicle, to generatemodified harmonic cancellation signals to minimize signals detected atthe one or more microphones 142.

Each of the adaptive filters 140 has associated with it a leakageadjuster 144 (one shown), a coefficient calculator 146, a cabin filter148, and a control block 150. For simplicity, only a single adaptivefilter 140, leakage adjuster 144, coefficient calculator 146, cabinfilter 148, and control block 150 are shown; however, these elements maybe replicated and used to generate and modify a noise reduction signalfor each harmonic to be cancelled or reduced.

The control blocks 150 control the operation of the associated harmoniccancellation elements, for example by activating or deactivating the EHCmodule 128 or by adjusting the amount of noise attenuation. The cabinfilters 148 model and compensate for a transfer function thatcharacterizes the combined effect of some electro-acoustic elements, forexample, the speaker(s), the microphone(s) 142, and of the environmentwithin which the EHX sub-system 112 operates. The adaptive filters 140,the leakage adjusters 144, and the coefficient calculators 146 operaterepetitively and recursively to provide streams of filter coefficientsto modify the individual harmonic cancellation signals. Suitableadaptive algorithms for use by the coefficients calculators may be foundin Adaptive Filter Theory, 4th Edition by Simon Haykin, ISBN 013091261.The leakage adjusters 144 select a leakage factor to be applied by thecorresponding one of the coefficient calculators 146. A leakage factoris a factor applied in the corresponding one of the adaptive filters 140to an existing coefficient value when the existing coefficient value isupdated by an update amount. Information on leakage factors may be foundin Section 13.2 of Adaptive Filter Theory, 4th Edition by Simon Haykin,ISBN 013091261.

The modified harmonic cancellation signals are then provided to thevehicle sound system 108 and transduced to acoustic energy by thespeakers. In some cases, the modified harmonic cancellation signals maybe combined with each other and/or with the gain adjusted harmonicsignals before being provided the vehicle sound system 108.

All or some of the harmonic cancellation reference signal generator 138,the adaptive filters 140, the leakage adjusters 144, the coefficientcalculators 146, the cabin filters 148, and the control blocks 150 maybe implemented as software instructions executed by one or moremicroprocessors or DSP chips, which may be components of an amplifier.

For achieving a natural sound, it can be beneficial to process the loadinformation used for controlling a level of the engine sound (e.g.,enhanced or canceled).

In this regard, the load processing module 122 receives an input signalrepresentative of engine load from the vehicle CAN bus 104 and convertsit to control parameters 116 which are provided to the level controlmodule 126.

The load processing module 122 is used for determining the inherentengine sound level to properly balance the sound augmentation. A signalrepresenting engine load is well suited for controlling soundaugmentation level for at least two reasons. First, overall engine noiselevels increase monotonically with increasing positive engine loads.Second, strong enhancement and/or the generation of new harmonics istypically desirable only for positive engine loads, when the enginepropels the transmission. Negative engine loads occur when thetransmission propels the engine, also known as engine brake. While theremay be high levels of inherent engine noise for during engine brake,noise cancellation may be desired for this situation but significantsound enhancement (including the generation of new harmonics) is rarelydesired.

The vehicle CAN bus 104 will typically have available several of thefollowing signals which correlate well with the engine load and may beavailable to the load processing module 122 either in analog or digitalform, for example, accelerator pedal position (APP); throttle positionsensor (TPS); mass air flow (MAF); manifold absolute pressure (MAP);engine torque; and/or computed engine load.

The load processing module 122 may convert the input signal from anative data form to a form more useful to the EHX sub-system 112. Forexample, if the engine load signal is representative of the enginetorque, the load processing module 122 may convert the torquemeasurement to an engine load measurement. The engine load may beexpressed as an index; for example, the maximum engine load may beexpressed as a number from 1-100. Likewise, the load processing module122 may, alternatively or additionally, convert other parameter valuesignals from a native form into a form more useful by the EHX sub-system112.

The level control module 126 receives the control parameters 116 asinput from the load processing module 122. Based on the input from loadprocessing module 122, the level control module 126 determines a gain tobe applied by corresponding harmonic gains 136, thereby providing adifferent harmonic shape depending on engine load. The input from thelevel control module 126 may also be used in the control loop of the EHCmodule 128, possibly for adjusting the leakage factor provided by theleakage adjuster 144 or for utilization by the coefficient calculatorblock 146. In the latter case, the error used in the coefficient updatealgorithm will be computed relative to a predefined harmonic shape,which can scaled based on the input received from the level controlmodule 126.

All abrupt transitions in the signals used for harmonic generation orcancellation, can be smoothed or introduced gradually, in order to avoidany distortions in the acoustic domain.

Based on a desired engine sound for a vehicle, one can predefine gearratios to be used within the virtual gearbox definition and RPMcomputation module 120 and the sound targets for each harmonic that isgenerated, enhanced or canceled by the EHX sub-system 112.

There are several ways to change the engine sound, to induce a change inthe perceived pitch of such sound, when a vehicle accelerates but theengine RPM remains constant. For example, a first approach is to use avirtual RPM (RPM virtual) to control perceived pitch changes. Thisvirtual RPM is based on a virtual gear box with fixed gear ratios.

A second approach is to use a control RPM (RPM_(control)), whichalternates between the virtual RPM and the actual engine RPM(RPM_(actual)), to control perceived changes in engine sound pitch. Thevirtual RPM is based on a virtual gear box with fixed gear ratios. Thecontrol RPM, when used to control the sound of the engine, uses thevirtual RPM only when the actual engine RPM remains relatively constant.In all other conditions, the control RPM is the actual engine RPM.

A third approach is to use a control RPM, using both the virtual RPM andthe actual engine RPM, as described above, but have the virtual RPMcomputed using time dependent discrete gear ratios instead of predefinedvirtual fixed gear ratios.

Pitch Shifting Controlled by Virtual RPM

In the first approach, a virtual RPM (RPM virtual) is computed in thevirtual gearbox definition and RPM computation module 120 and is thesingle piece of information used to induce a shift in the perceivedpitch of the engine sound, regardless of the actual engine RPM. In thiscase, the control RPM that is provided to the EHX sub-system 112corresponds to the virtual RPM.

For example, a current CVT gear ratio, GR_(CVT), may be defined as:

$\begin{matrix}{{{GR}_{CVT}(t)} = {\frac{{RPMactual}(t)}{{VSP}(t)} \cdot {CR}}} & (1)\end{matrix}$

where t is time and CR is a constant that captures all the fixedtransmission ratios external to the gearbox, such as the reardifferential transmission ratio, tire circumference, and so forth. TheCVT gear ratio varies continuously in time.

A vehicle manufacturer can predefine a set of fixed gear ratios, towhich the virtual gearbox definition and RPM computation module 120 canmap the variable CVT gear ratios (GR_(CVT)). For example, if ƒ(⋅) is amapping function, c is a constant, a virtual gear ratio,GR_(virtual)(t), may be computed as follows:GR_(virtual)(t)=c·ƒ(GR_(CVT)(t)  (2)

The mapping function may then be expressed as:

$\begin{matrix}{{f\left( {{GR}_{CVT}(t)} \right)} = \left\{ \begin{matrix}{{\mathcal{g}}\; r_{1}} & {,{if}} & {{th}_{1} \leq {{GRcvt}(t)}} \\{{\mathcal{g}}\; r_{2}} & {,{if}} & {{th}_{2} \leq {{GRcvt}(t)} \leq {th}_{1}} \\\; & \vdots & \; \\{{\mathcal{g}}\; r_{N}} & {,{if}} & {{{GRcvt}(t)} \leq {th}_{N}}\end{matrix} \right.} & (3)\end{matrix}$

where {gr_(N)} is the set of fixed virtual gear ratios and {th_(N)} isthe set of predefined gear ratio thresholds. In some cases, the constantc may be set to one. In the tuning process, it can be used as a simpleway to scale the gear ratios, if desired, without changing the thresholdthy. The constant c controls the slope at which the virtual RPMincreases.

The virtual RPM, RPM_(virtual)(t), can then be computed by the virtualgearbox and RPM computation module 120 as:RPM_(virtual)(t)=GR_(virtual)(t)·VSP(t)·CR⁻¹  (4)

In this example, the virtual RPM computation is based on a set ofpredefined, virtual, gear ratios. The values of these gear ratios aretunable within the engine sound control module 106 by a vehiclemanufacturer to achieve a desired engine sound. A signal representativeof the virtual RPM is provided to the EHG module 124 which generatessine-wave reference signals that are proportional to the harmonics ofthe virtual RPM. The harmonics signals can then be transduced toacoustic energy via speakers in the vehicle sound system 108, thereby toproduce an engine sound in the vehicle cabin via the vehicle soundsystem 108.

As shown in FIG. 2, an exemplary graph 200 illustrates a sample gearratio mapping using the principles described above. The graph 200 plotsgear ratio 210 versus time 212. The gear ratio 210 values range from alow of 0.2 to a high of 2.0. Predefined gear ratio thresholds 214 a-gare shown as dotted lines from time=0 to time=35. As time 212 increases,an actual gear ratio 216 increases initially and then decreases, whilethe virtual gear ratios 218 remain more constant while increasing anddecreasing, illustrating a more step-like progression similar to amanual gear box. In the CVT engine, the actual gear ratio 216 variescontinuously over time.

Pitch Shifting Controlled by Alternating Control RPM

As mentioned above, pitch shifting may be controlled using a control RPMthat alternates between the calculated, virtual RPM and the actual,measured engine RPM (RPM_(actual)), rather than using the virtual RPMalone. In this approach, the virtual gearbox definition and RPMcomputation module 120 may include control RPM selection logic whichalternates the control RPM the actual engine RPM (RPM_(actual)) and thevirtual RPM virtual) according to a set of criteria including drivingsituation and actual engine parameters. One exemplary set of criteria isshown in FIG. 3 in Table 1. In Table 1, VSP represents actual vehiclespeed. The set of criteria represent how the virtual gearbox definitionand RPM computation module 120 determines the control RPM as the VSPremains constant, increases or decreases, in conjunction with an engineRPM as it increases, decreases or remain constant. For example, as seenin Table 1, a main CVT engine sound problem is generally associated witha condition of the VSP increasing and the RPM remaining constant. Whenthis occurs, the virtual gearbox definition and RPM computation module120 sets the control RPM to the virtual RPM. The control RPM is providedto the EHX sub-system 112.

In other examples, a rate of change in actual engine RPM or vehiclespeed may be used to improve performance. In addition, engine loadconditions may be taken into consideration.

As shown in FIG. 4, an exemplary control RPM selection process 400residing in the virtual gearbox definition and RPM computation module120 that implements the decisions shown in Table 1 of FIG. 3 includesdetermining 402 whether a change in actual RPM (ΔRPM) is greater than apredefined maximum R_(max). If ΔRPM is greater than R_(max), the vehicleRPM is increasing and process 400 sets 404 the control RPM equal to theactual RPM.

If ΔRPM is less than R_(max), process 400 determines 406 whether ΔRPM isgreater than a predefined minimum rate R_(min).

If ΔRPM is less than the predefined minimum rate R_(min), the actual RPMis decreasing and process 400 determines 408 whether a change in actualvehicle speed (ΔVSP) is greater than a predefined maximum vehicle speedV_(max).

If ΔVSP is less than V_(max), actual vehicle speed is not increasing andprocess 400 sets 410 the control RPM equal to the actual RPM.

If ΔVSP is greater than V_(max), actual vehicle speed is increasing andprocess sets 412 the control RPM equal to the virtual RPM(RPM_(virtual)).

If process 400 determines 406 that ΔRPM is greater than R_(min), the RPMis constant and process 400 determines 414 whether ΔVSP is greater thanV_(max).

If ΔVSP is less than V_(max), the vehicle speed is decreasing andprocess 400 sets 416 the control RPM equal to the actual RPM. If ΔVSP isgreater than V_(max), the actual vehicle speed is increasing and process400 sets 418 the control RPM equal to the virtual RPM.

It is important for the control RPM selection process 400 to exclude anabrupt increase in RPM because such behavior does not occur in actualvehicles. An abrupt decrease in RPM is permissible because itcorresponds to an up-shift.

Pitch Shifting Controlled by Alternating Control RPM Using TimeDependent Discrete Gear Ratios

One alternative example to the fixed gear ratio mapping described aboveis to freeze the current gear CVT ratio when an engine sound correctionis needed. That is, the virtual fixed gear ratio can be set to aninstantaneous value of the current gear ration, GR_(CVT)(t₀), at a time(t₀) when the determination that engine sound correction is needed ismade. The determination as to whether sound correction is needed may bemade by way of the control RPM selection process described above withrespect to FIG. 4, in which the control RPM is set to the virtual RPMwhen sound correction is needed. If the gear ratio is fixed, the virtualRPM (RPM_(virtual)) increases as the vehicle speed increases, thusproducing an engine sound in such a way that the perceived pitch isincreasing. The gear ratio is set back to the actual gear ratio valuewhen the gear ratio variation exceeds a gear ratio virtual deviationvalue. A gear ratio deviation of the virtual gear ratio (GR) to a CVT GRmay be defined as:

$\begin{matrix}{{\Delta\;{{GR}(t)}} = {c \cdot \frac{{{GR}_{virtual}(t)} - {{GR}_{CVT}(t)}}{{GR}_{virtual}(t)}}} & (5)\end{matrix}$

Where c is a constant. This gear ratio deviation can be used tointroduce abrupt steps in the virtual gear ratio evolution in time.

$\begin{matrix}{{{GR}_{virtual}(t)} = \left\{ \begin{matrix}{{{GR}_{virtual}\left( {t - 1} \right)},{{if}\mspace{14mu}{correction}\mspace{14mu}{needed}},{{{and}\mspace{14mu}\Delta\;{{GR}\left( {t - 1} \right)}} < A}} \\{{{GR}_{CVT}(t)},{otherwise}}\end{matrix} \right.} & (6)\end{matrix}$

The parameter A is tunable and represents the virtual vs. actual gearratio deviation that triggers a gear shift.

An alternative to the above is to use a fixed gear ratio deviation:ΔGR(t)=c·(GR_(desired)(t)−GR_(CVT)(t))  (7)

where c is a constant, which can be selected as discussed above.

The rate by which the pitch shifts can be varied, not only based on thespeed of the vehicle, but based on the load. In this approach, themapping function described above is varied by changing the constant cwith the engine load or the vehicle acceleration. Thus c in equations(2), (5), and (7) becomes a variable, c(t), that varies as a function ofactual engine load:c(t)=ƒ(EngineLoad(t))  (8)

that of the driver's intent, i.e. the accelerator position:c(t)=ƒ(AcceleratorPosition(t))  (9)

or a combination of the two:c(t)=ƒ(EngineLoad(t),AcceleratorPosition(t))  (10)

In the simplest case, the function ƒ(⋅), would be a linear function.

Other possible applications for the CVT sound controls

The algorithms described above can be used in programming the mode ofoperation of an actual CVT, thus obtaining the desired pitch shift inthe engine sound. In this case, the use of EHC and EHE based on theactual engine RPM could be enough to control the overall sound withinthe passenger cabin. Perceptual pitch shifting techniques can still beused, if needed.

Additionally, the techniques described above may be adapted to electricvehicles and/or hybrid vehicles running in electric mode.

When applying the previously described sound control techniques inelectric vehicles, a virtual RPM can be determined based on vehiclespeed (VSP) and predefined virtual gear ratios.

A minimum RPM and a maximum RPM can be defined. The minimum RPM and themaximum RPM can then be used as shifting points in the virtual gearbox.In some cases, the minimum RPM and the maximum RPM can be constant intime.

A virtual gear for the electric vehicle can then be computed as follows:

$\begin{matrix}{{{where}\mspace{14mu}{{GR}_{virtual}(t)}} = \left\{ \begin{matrix}{{\mathcal{g}}\; r_{i + 1}} & {,{if}} & {{{RPM}_{virtual}\left( {t - 1} \right)} \geq {RPM}_{\max}} \\{{\mathcal{g}}\; r_{i - 1}} & {,{if}} & {{{RPM}_{virtual}\left( {t - 1} \right)} \leq {RPM}_{\min}} \\{{\mathcal{g}}\; r_{i}} & {,{if}} & {{RPM}_{\min} < {{RPM}_{virtual}\left( {t - 1} \right)} < {RPM}_{\max}} \\{{\mathcal{g}}\; r_{1}} & {,{if}} & {{{{RPM}_{virtual}\left( {t - 1} \right)} \leq {RPM}_{\min}},{{{and}\mspace{14mu}{{GR}_{virtual}\left( {t - 1} \right)}} = {{\mathcal{g}}\; r_{1}}}}\end{matrix} \right.} & (11)\end{matrix}$

At any time, if VSP=0, the virtual gear will be switched to neutral,which will result a GR_(virtual)(t)=0. That is, for VSP=0, the virtualgearbox will be in neutral, with a gear ratio gr₀ of 0. In this case,MRP_(virtual)(t)=0. Once the vehicle starts moving, and the VSP>0, thevirtual gearbox will shift into first gear, which has a gear ratio ofgr₁.

In some cases, the minimum and maximum RPM threshold values can vary intime and can increase and decrease based in the vehicle acceleration. Ifthe acceleration is high the RPM thresholds will be high, if theacceleration decreases the RPM limits will be lower.

A virtual RPM (RPM_(virtual)) for the electric vehicle can then becalculated according to equation (4), above (i.e.,RPM_(virtual)(t)=GR_(virtual)(t)·VSP(t)·CR⁻¹). The virtual RPM can thenbe provided as input to an EHG module of an EHX sub-system (such asdiscussed above). Signals produced by the EHX sub-system, based on thevirtual RPM and input received from input control logic, are transducedto acoustic energy by one or more speakers within a vehicle sound systempositioned within an interior of a vehicle and provide a desired sonicexperience.

In some cases, the actual RPM of the electric motor may be provided toan EHC module of the EHX sub-system. Alternatively, in some cases, theelectric vehicle may not utilize an EHC module.

The application of these techniques in hybrid vehicles enables acreation of a continuous sound for when the vehicle operates in bothinternal combustion (IC) mode and electric vehicle mode (EV). In EVmode, the EHG module will operate on a virtual RPM that can becalculated based on vehicle speed and predefined virtual gear ratios(e.g., a first set of predefined virtual gear ratios as provided inequation 11) as discussed above with reference to electric vehicles. InIC mode, the EHG module can operate on the actual engine RPM (i.e.,measured from the combustion engine) if sound correction is notnecessary; or, if sound correction is necessary, then the EHG module canoperate on the virtual RPM which can be determined according toequations (1) through (4) above based on based on the actual, measuredRPM of the internal combustion engine, vehicle speed, and predefinedvirtual gear ratios (e.g., a second set of predefined virtual gearratios as provided in equation 4).

For electric vehicles or hybrid vehicles operating in EV mode, the loadprocessing module may receive a signal representative of the acceleratorpedal position and convert it to control parameters which can beprovided to the level control module.

Psychoacoustic Approach to Pitch Shifting

The control algorithm described in this document can be used to drivepitch shifting based on pitch circularity perception. In one approach,pitch can be shifted by manipulating constant frequency harmonics. Forexample, if signal x(t) is a sum of harmonics of a fundamentalfrequency, then to shift the perceived pitch, the even harmonics or oddharmonics can be gradually discontinued (e.g., by cancelling thoseharmonics via the EHC module) starting at the point the pitch shift isdesired.

This approach is illustrated in the spectrogram 500A of FIG. 5A for thediscontinuation of even harmonics 510, and the spectrogram 500B of FIG.5B for the discontinuation of odd harmonics 512. The examples,illustrated in FIGS. 5A and 5B show certain harmonics of a substantiallyconstant fundamental frequency, such as would be the case when theactual RPM levels off even as the vehicle speed continues to change. Theharmonics being discontinued can be canceled via the EHC module 128.Thus, in some cases, a shift in perceived pitch may be achieved viacancellation of harmonics alone.

Alternatively or additionally, a shift in the perceived pitch may beinduced by adding harmonics in between the existing ones. The EHG modulecan be utilized to generate the harmonics at the necessary level toinduce the perceived pitch shift.

Alternatively or additionally, engine harmonic enhancement (EHE) can beused for the same purpose, by enhancing certain harmonics of afundamental frequency, such as even harmonics, or every full orderharmonic. The goal is to create specific ratios between neighboringharmonics, thus creating the shift in perceived pitch.

In yet another approach, illustrated in the spectrogram 600 of FIG. 6,an eternally increasing pitch can be achieved by playing harmonics in alimited frequency range. The spectrogram 600 of FIG. 6 shows a set ofsine waves 610 of increasing frequency. When the frequency of a sinewave 610 approaches the upper preset frequency limit, the amplitude ofthat sine wave starts decreasing until it completely disappears. Aboutthe time that sine wave 610 ends playing, a new sine wave 610, of a lowfrequency will start playing. This new one will increase in frequencyuntil it approaches the maximum one, at which point it will graduallydecrease in level, until it becomes inaudible. This process continuesfor as long as it is desired.

The sine waves 610 are harmonics of a fundamental frequency that isincreasing with time. “Harmonics” as used herein can include fractional(e.g., half harmonics or quarter harmonics) or full order harmonics. Thefundamental frequency may, for example, be representative of the virtualRPM discussed above, or an actual vehicle RPM that increases with time.

This technique illustrated in FIG. 6 may be utilized, for example, witha vehicle equipped with an electric motor, in which case the fundamentalfrequency may be representative of an actual RPM of the electric motor.For example, the fundamental frequency may be determined from an actualmeasured RPM from the electric motor. In some cases, the electric motormay directly drive the wheels of the vehicle such that the vehicle speedvaries linearly with the RPM of the electric motor, in which cases thefundamental frequency may be calculated based on a measured vehiclespeed.

A signal representative of the fundamental frequency can be the input toan engine harmonic generation module, such as described above withrespect to FIG. 1B, and a level control module, such as described abovewith respect to FIG. 1B, can be used to adjust respective gains appliedto the individual harmonics of the fundamental frequency (e.g., based onmeasured vehicle parameters such as accelerator pedal position) suchthat the individual harmonics are only reproduced over the desiredfrequency range.

While the above describes a particular order of operations performed bycertain examples, it should be understood that such order is exemplary,as alternative examples may perform the operations in a different order,combine certain operations, overlap certain operations, or the like.References in the specification to a given example indicate that theexample described may include a particular feature, structure, orcharacteristic, but every example may not necessarily include theparticular feature, structure, or characteristic.

While given components of the system have been described separately, oneof ordinary skill will appreciate that some of the functions may becombined or shared in given instructions, program sequences, codeportions, and the like.

The foregoing description does not represent an exhaustive list of allpossible examples consistent with this disclosure or of all possiblevariations of the examples described. A number of examples have beendescribed. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe systems, devices, methods and techniques described here.Accordingly, other examples are within the scope of the followingclaims.

A number of examples have been described. Nevertheless, it will beunderstood that additional modifications may be made without departingfrom the scope of the inventive concepts described herein, and,accordingly, other examples are within the scope of the followingclaims.

What is claimed is:
 1. A method comprising: in a vehicle equipped with acontinuously variable transmission (CVT) and a vehicle sound system,determining if sound correction is necessary; and if sound correction isnecessary, generating one or more harmonic signals based on an actual,measured RPM, the one or more harmonic signals being proportional toharmonics of the actual RPM, and, in the vehicle sound system,transducing the one or more harmonic signals to acoustic energy tothereby produce a shift in perceived pitch within the vehicle byreducing a harmonic sound produced by an engine of the vehicle or byadding a harmonic sound between harmonic sounds produced by the engineof the vehicle while the pitch of harmonic sounds produced by the engineof the vehicle remain substantially constant.
 2. The method of claim 1wherein determining if sound correction is necessary comprises:determining that a change in actual RPM (ΔRPM) does not exceed a maximumvalue Rmax; and determining that a change in actual vehicle speed (ΔVSP)exceeds a minimum value Vmax.
 3. The method of claim 2 whereindetermining if sound correction is necessary further comprisesdetermining that ΔRPM exceeds a minimum value Rmin.
 4. An engine soundmanagement system of a vehicle equipped with a continuously variabletransmission (CVT) and a vehicle sound system, the engine soundmanagement system comprising: circuitry for determining if soundcorrection is necessary, and if sound correction is necessary, forgenerating one or more harmonic signals based on an actual, measuredRPM, the one or more harmonic signals being proportional to harmonics ofthe actual RPM; and circuitry for causing the vehicle sound system totransduce the one or more harmonic signals to acoustic energy to therebyproduce a shift in perceived pitch within the vehicle by reducing aharmonic sound produced by an engine of the vehicle or by adding aharmonic sound between harmonic sounds produced by the engine of thevehicle while the pitch of harmonic sounds produced by the engine of thevehicle remain substantially constant.
 5. The system of claim 4 whereincircuitry for determining if sound correction is necessary comprises:circuitry for determining that a change in actual RPM (ΔRPM) does notexceed a maximum value Rmax; and circuitry for determining that a changein actual vehicle speed (ΔVSP) exceeds a minimum value Vmax.
 6. Thecircuitry of claim 5 wherein the circuitry for determining if soundcorrection is necessary further comprises circuitry for determining thatΔRPM exceeds a minimum value Rmin.